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Photodetectors allow monitoring of a volume of space without blocking the use of that space. Indoors, photodetectors have been used in security applications to detect the presence of unauthorized persons. The use of photodetectors outdoors has been somewhat limited because it can be difficult to distinguish a feature from the natural variations in ambient light caused by changes in sunlight or the orientation of the monitored volume to the sunlight. Ways to overcome the difficulties in using photodetectors outdoors have included filtering, use of regions of the electromagnetic spectrum not affected by sunlight, and imparting unique characteristics to the light being used in the system.
Infrared (IR) sensoring techniques offer many advantages for products that have automotive, industrial and retail applications. However, many of these systems must operate in the presence of sunlight, which has the potential to significantly reduce the performance of the IR sensor. Thus, there is a great need to identify the presence of sunlight or other interfering ambient light and provide corrective techniques to reduce or eliminate the impact of the sunlight on the performance of the IR sensor.
Closures for apertures such as vehicle windows, sunroofs and sliding doors are now commonly motor driven. As a convenience, power windows are frequently provided with control features for the automatic closing and opening of an aperture following a simple short command, commonly known as an xe2x80x9cexpress closexe2x80x9d feature. For instance, a driver""s side window may be commanded to rise from any lowered position to a completely closed position simply by momentarily elevating a portion of a window control switch, then releasing the switch. Alternatively, automatic closing and opening of an aperture may be in response to input from a separate device, such as a rain or temperature sensor. Such automated aperture closing features may also be utilized in various other home or industrial settings.
While the features described above provide added convenience, they may also introduce a safety hazard. Body parts or inanimate objects may be present within an opening when a command is given to automatically close the window or door. For example, an automatic window-closing feature may be activated due to rain impinging on an interconnected rain sensor while a pet has its head thorough the window. A further example includes a child who has placed its head through the opening of a window or sunroof that is activated to close by the driver, another passenger or accidentally by the child.
Systems have been developed to avoid potentially tragic accidents or property damage involving intervening objects trapped by power windows or sunroofs. These systems, using contact methodologies, typically detect the circumstance in which a window has been commanded to express close when it should not. Complete closure is prevented whenever an intervening object such as a finger or arm extended through the opening contacts the safety system during closure. In further refinements of the closure safety system, the closure member, such as the window, is not required to come into contact with the intervening object for the object to be detected.
When sunlight can be disregarded, such contactless object detection systems typically measure the magnitude of a reflected signal to determine whether an intervening object is present. A photo-emitter emits a light beam, which an optical system directs across the opening that is being monitored. An unobstructed opening may result in the reflection of at least a portion of the emitted beam from the opposing side of the aperture. The reflection from the opposing side ordinarily results in a reflected signal of a well-defined intensity being returned to a receiver. A photo-receiver disposed in an appropriate location receives the reflected light beam and generates an output signal indicative of the intensity of the reflected beam. An intervening object located in the path of the light beam changes the intensity of the reflected light beam, a condition reflected in the receiver output signal. The receiver output signal therefore can be used to differentiate between the opening with an object through it and the opening unobstructed.
These optical systems, however, are vulnerable to interference by ambient light, especially sunlight. Prior art systems for coping with sunlight have included the use of synchronous detectors and xe2x80x9cjudgment circuitsxe2x80x9d consisting of a number of logic circuits coupled together. These judgment circuits, however, may still be susceptible to interfering sunlight and typically include several functional blocks, each of which contains several digital logic circuits. The large number of parts associated with the judgment circuits can increase both the power that is consumed and dissipated as heat and the cost associated with the object detection circuitry.
An improved way to cancel the portion of a signal that is associated with sunlight, while maintaining the intelligibility of the portion of the signal associated with an obstacle, is needed. Preferably, such an apparatus will provide enhanced accuracy by reducing the effect of the interfering ambient light while using fewer parts and consuming less power than the prior art.
The present invention has particular application in systems providing an indication of the presence of an object within a pinch zone located in the path of an automated closure device such as a powered window, powered sunroof, or powered door or hatch. When an optical sensor incorporates a synchronous detection amplifier operating in the infrared (IR) range to selectively amplify the system light signal, the invention negates the effect of sunlight that could otherwise swamp the desired light or cause excess electronic noise.
The embodiments of the invention work in conjunction with methods and apparatus for sensing an object with an optical sensor. The optical sensor utilizes synchronous detection and an integrator to separate a desired optical signal from ambient light and electronic noise. Further, the system cancels modulated energy from features of the environment not associated with an object in the opening.
The sunlight compensating system functions with a system that includes a modulator driving a photo-emitter and a switched amplifier receiving first and second signals respectively. A photodetector receives a portion of light reflected from the pinch zone and/or an object therein and provides an optical detector signal to the switched amplifier.
The switched amplifier provides an output signal that includes a voltage that results from the difference between the optical detector signal and a reference signal multiplied by a gain that is dependent on the phase in the detection cycle. The gains and duration of the phases are selected to set the gain of the switched amplifier to an average value of zero when no modulated optical signal is present from the pinch zone and/or object therein.
The obstacle detection system further includes a means to electronically integrate the difference between the output of the switched amplifier and an adjustable reference voltage for a predetermined measurement time. A detector receives the integrator output signal and provides indicia of the presence or absence of an object within the pinch zone.
The obstacle detection system further includes a control element or controller that provides the means to monitor the degree of photodetector exposure to sunlight and then apply appropriate control signals that selectively optimize the system response and compensate for changes to the transfer function of some components.
In one embodiment the controller functionality may be implemented using a conventional microcontroller integrated circuit and the appropriate analog processing elements such as analog to digital converter (A/D), digital to analog converter (DAC), and digital to resistance converter, (RDAC). These elements may be part of the microcontroller functionality or may be implemented discretely. Alternate embodiments of the controller may be implemented using digital logic devices in conjunction with the analog processing elements enumerated above.
In one embodiment of the system, an optical source and optical detector are optically coupled to monitor a target area that reflects at least a portion of an optical signal. The optical detector detects a received optical signal having temporal characteristics allowing the received signal to be distinguished from ambient light. The optical detector provides a detector output signal indicative of one characteristic of the received optical signal to a conditioning circuit for outputting a digital output representative of the detector output signal. A controller for receiving the digital output from the conditioning circuit determines the magnitude of an ambient light-induced signal in the digital output and outputs a control signal to a second input of the conditioning circuit, that uses the second input as an error compensating offset.
In another embodiment, the optical object sensing apparatus capable of compensating for the effect of ambient light comprises an optical source and detector, a conditioning circuit, and a controller. The optical source and detector are optically coupled for monitoring a target area that reflects at least a portion of an optical signal for detection as a received optical signal. The optical detector provides a detector output signal indicative of one characteristic of the received optical signal. The conditioning circuit outputs a first digital output representative of the detector output signal and a second digital output representative of an integrated output signal. The controller receives the first and second digital outputs, and determines an effect of the ambient light on the integrated output signal from said first and second digital outputs. The controller also outputs a detection output.
When the sunlight dominates the incoming photocurrent such that the preamplifier is saturated, one embodiment of the sunlight compensating system outputs an offset, designed to bring the preamplifier out of saturation, to the detection system before determining the compensation based on the sunlight remaining in the incoming signal. Another embodiment uses a low-gain buffer to detect the magnitude of the sunlight-induced signal. The output of this buffer is used to bring the incoming signal into the range for the signal compensation.
One method for canceling the effect of ambient light in an optical object sensing apparatus comprises optically coupling an optical source and detector for monitoring a target area that reflects at least a portion of an optical signal for detection as a received optical signal. The optical detector provides a detector output signal indicative of one characteristic of the received optical signal. The optical object sensing apparatus outputs a digital output representative of the detector output signal from a conditioning circuit. The digital output from the conditioning circuit is received at a controller. The controller determines the magnitude of an ambient light-induced signal in said digital output and outputs a control signal to the conditioning circuit. The conditioning circuit adjusts the digital output to compensate for the ambient light-induced signal based on the control signal.
An alternate method for canceling the effect of ambient light on an optical object sensing system comprises optically coupling an optical source and detector for monitoring a target area that reflects at least a portion of an optical signal for detection as a received optical signal. The optical detector provides a detector output signal indicative of one characteristic of the received optical signal. A conditioning circuit receives the detector output signal and outputs a first digital output representative of the detector output signal and a second digital output representative of an integrated output signal. A controller adapted to determine an effect of the ambient light on the integrated output signal receives the first and second digital outputs and outputs a detection output based upon the first and second digital outputs.
In a further embodiment, a controller interprets the digital reading of ambient light intensity utilizing a previously measured relationship between the ambient light and the detector output. The controller then removes the effects of the ambient light from the detection system""s digital output. Other aspects, features, and advantages of the present invention are disclosed in the detailed description that follows.